1. Field of the Invention
This invention relates to chains and more particularly to sludge collector chains having snap-lock pins.
2. Description of Related Art
Sludge collectors are commonly used in wastewater treatment plants to scrape the settled sludge from the bottom of the settling tank and also to skim floating waste off the surface of the wastewater. These sludge collectors typically include a number of sludge flights, which are usually elongated members that extend the width of the tank. The ends of the flights are connected to conveyor chains which carry the flights in a circuit lengthwise along the bottom of the tank and back over the surface of the water to perform the scraping and skimming functions. The tanks are typically made of concrete and have supporting shafts with bearings and locking collars which support the transmission sprockets. The transmission sprockets, in turn, power the conveyor chain and flight systems.
These systems have been supplied for over seventy five years. The chains utilized in the systems up until the late 1970's were typically either cast steel, cast iron, malleable iron, welded steel, ductile iron, or other metallic materials. As a result, these chains were rather heavy, weighing up to seven pounds per foot. They were also subject to very high corrosion rates when taken out of service or exposed to the atmosphere after having been submerged in wastewater or water treatment basins. Due to weight, they may become extremely difficult to handle and maintain, generally requiring teams of maintenance personnel and portable cranes.
In the 1970's, non-metallic chains were introduced into the wastewater industry. They were readily accepted as they weigh approximately one-fifth that of the previous metallic chains, but the ultimate strengths of the product are approximately one-tenth to one-fifteenth that of the metal chains. Although applications can be limited, municipalities or end users have continued to specify them because the drive units required to drive the systems have much lower horsepower requirements due to the significantly lower weight and, therefore, have much lower power demands, even though the strength issue may eliminate certain applications. The ease of maintenance, however, is the primary reason non-metallic chains dominate the wastewater industry.
It is desirable to have a non-metallic conveyor chain which exhibits good strength characteristics, is lightweight, and is relatively easy to assemble. It is further desirable to have a non-metallic conveyor chain design which is able to isolate the wearing parts of the chain assembly for future replacement of the wearing parts only so as to not require complete chain replacement.